E30 Zone

Hi everyone,
Iv got a 325i can auto. If I put the car in drive and the setting in either 'S' or 'E' it won't change gear.
If I place the selector in '1,2,3' then it will give me manual gears.
Any ideas?
Is there a relay, solenoid, fuse etc that would cause this fault?
It drove fine when I jumped in it after work then just lost gears after a couple of minutes.
Please help,
Thanks in advance.
Steve

The ecu could possibly cause this issue. It is located in the n/s/r of the boot . Most common issue back in the day was oil contamination in the gearbox loom wiring plug where it attaches to the gearbox. The plug is on the n/s and is accessed from underneath. It has a threaded locking type connector.
If there is oil present when undone, that may be your issue. Cleaning it with brake cleaner will buy you some time but ideally the seal where the plug attaches to the box needs replacing.

Thank you Pete,
I have just had a look at the ECU, no loose connector that I could see.
I then had a look at the switch on the NS of the gearbox, after unscrewing the connector oil was present.
I tried to clean it in place without removing it. I then sprayed it with WD40 but no difference.
Do you know the name of the switch?
Thanks again for your help
Steve